Is This Enough Filtration?

Just the espeis, cpd's and cories make you 100% stocked, then you want to add more fish on top of that. Stocking is not about the amount of filtration, it is about the number, size, bioload and compatibility of the fish. Your list checks the compatibility and size boxes but it does not check the number and bioload boxes.
Reduce the numbers of each species by half or lose one completely and reduce the rest by about a third and you'll be OK.

The good thing is that you have chosen fish that are good in a short tank. You said it was 20 gall tall, which means it as not a long as a standard. 20 galls is around 70 litres, how long is the tank?

Sorry, I meant to say 20 long not 20 standard. We don't use those terms in the UK, I only know about tall and long from reading other forums which have American members.

What stocking ultimately comes down to is getting fish that a) get along with each other b) have a big enough tank c) have their species needs met d) the amount of them don't crowd the tank or add too much waste to the tank.

a) is quite simple - will this fish eat that fish; will these fish fight and probably kill each other; have I got more female livebearers than males because males harass females; and so on.

b) this is quite simple too. A tank should be at least 5 times longer that a fish's full adult size and 1.5 times wider. This applies mainly to very large fish and is to allow a fish room to move. And fast swimming fish need a much larger tank than you'd think from the size of the fish. Like zebra danios which can cross a 4 foot tank in less than a second need a tank longer than 24 inches.

c) this gets more complicated as you have to research the fish. Shoaling fish need to be in a group. Hard alkaline water fish need hard alkaline water and shouldn't be put in soft acid water with a lot of soft acid loving fish. Cave dwelling/spawning fish need caves. Fish that sift the substrate for food do better with sand. Fish that hide in the substrate do better with sand. Timid fish need lots of places to hide.

d) this is the most complicated of all. Animals are made of a lot of proteins which contain nitrogen. Different species use different ways to get rid of nitrogenous breakdown products. We turn them into urea which is dissolved in water to make urine. Birds turn it into uric acid which comes out with their poo. Fish turn it into ammonia which comes out through their gills. The filter turns this ammonia into nitrate and we have to do water changes to get rid of it. The more fish there are and the messier the fish are, the faster this nitrate builds up so the bigger and more often we have to do water changes to get rid of it.
But their is more in our urine than just urea. Have you ever had a sample of urine sent off for testing, or know anyone who has? I once worked in a hospital lab and we tested for many things in urine. Fish make their versions of these things as well, and they excrete them into the tank water. The filter does not remove these chemicals, they build up in the water like nitrate. And some of these chemicals can affect the fish. Too many fish results in stress from high levels of these chemicals. This is why we try not to over stock our tanks. It's not about how many fish can I fit in this tank but how many fish can I put in this tank without causing chemical stress.
I did say it got complicated.


With your tank being just 24 inches long, it does limit the species you can have because of lack of swimming room. The fish in your list should be OK; cories, cpd's espies and otos are not fast swimming fish that need a long tank. But I don't know about the killifish because I can't find out info from sites I trust. I'm not even sure which species you mean because lampeye killifish could be Aplocheilichthys kingii, Poropanchax normani, Aplocheilichthys normani, Micropanchax macrophthalmus to name a few that google finds for that name.

And I forgot to mention before about otos. These should only be put into a tank that has grown a lot of algae. They can be very picky eaters and can starve in a tank which doesn't have the kind of algae they like. Some people have managed to get them eating zucchini (courgette for UK members!) or sushi nori but not all otos will eat these. If your tank is not full of algae, wait to get the otos until it is.

I have not come across HOB filters in any of the shops I use; they are much more popular in the USA than here. So I googled yours to see what they are like, and couldn't find the 150's. I could only find aqua clears with numbers up to 110, even on Hagen's US website.
Can you tell me what the turnover of your filters is in litres per hour (it should give that figure on the packing or in the instructions) and what size tank Hagen says they are rated for?
The manual for the smaller filters say they have sponge, carbon and biomax. I would ditch the carbon and get more biomax or sponge. You don't need carbon full time but filter manufacturers still insist on using it.

But as long as the filters are rated for a tank the size you have, that's fine. Adding more filtration does not allow to to put more fish in the tank, well only a few more not a lot more. As I explained before, filters only remove ammonia and nitrite and with too many fish lots of other things will build up and harm the fish.


Norman's lampeye - it's not on Seriously Fish but I have found it on Badmans Tropical Fish. It says 10 galls is fine, but doesn't give a tank length. Though I've never seen a 10 gall longer than 24 inches, so they should be fine.

Otos are an awkward fish, they very often die within a couple of weeks of buying them. They are all wild caught, and those that survive the capture process are often kept in algae free containers till they are shipped. Once they reach a certain point of starvation they can't start eating again. When you buy otos, you should always wait until they've been in the shop at least 2 weeks so that the weak ones will already have died, then choose the ones with fat stomachs as those will be eating. The problem with getting them on-line is that you won't know what condition they are in and you do risk having them die in your tank.

If Aqua Clear 150s are rated for 30 galls, one will be more than enough for 20 galls. Putting 2 in won't make any difference to the number of fish you can keep in there.

If you get a bigger filter, you can have a few more fish. But double the filtration does not mean double the fish. And going from am internal to a canister filter means you can have more fish as an internal takes up space in the tank.

It is because of the biochemicals excreted and secreted by the fish. They are not removed by the filter - that only removes ammonia and nitrite. The more fish there are, the more of these chemicals that are in the tank. That's what you have to avoid and we do this by not overstocking.

Twice over the years (the last time was 2002, it happened just after we had double glazing installed which is how I remember) I have woken up to find every fish in my tank dead. At the time I had no idea what had happened. But since then we got broadband and I have made a point of educating myself; I am now pretty sure what happened to kill my fish. I was overstocked, I did water changes maybe every 3 weeks, and I have low carbonate hardness.
There were too many fish in the tank producing too much waste of all types. I didn't do enough water changes which meant the waste products built up - and I didn't have any live plants back then to help. With low KH, the acidic waste products used up all the KH leaving nothing to stop the pH crashing, which it undoubtedly did but not having a test kit back then I can't prove the last bit. But I did eventually get a test kit and that's how I know that my pH crashes if I don't do enough water changes.

I have twice woken up to dead fish through bad tank management and I don't like to think of anyone else going through the same thing.